1. Field of the Invention
The present invention relates to a small-capacity expansion valve used in small refrigerators to control a coolant flow.
2. Description of the Prior Art
Small refrigerating equipment incorporated in home refrigerators and automatic vending machines have a very small amount of cooling medium and hence often use a capillary as an expansion device. However, the capillary has a drawback of being unable to quickly respond to load changes.
When an expansion valve is used instead of the capillary, it is required to have a small capacity which matches that of the small refrigerating equipment and also have high reliability. For this end, it is necessary to significantly improve the machining precision of the needle valve disc and seat and to construct the valve so that the contact pressure between the valve disc and the valve seat will not become excessively large.
Under these situations, conventional expansion valves with a capacity suitable for small refrigerating equipment have a construction in which a valve disc is provided slidable in a primary chamber and urged by a small valve spring to close an opening in the valve seat provided in a separating wall between the primary and secondary chambers, and in which a communication rod that passes through the valve seat from the secondary side to push the valve disc toward the valve opening direction is connected to a pressure-activated mechanism.
FIG. 7 shows the construction of the above-mentioned prior art. A valve seat d is provided between a primary chamber b and a secondary chamber c in the expansion valve body a. A needle valve disc e that is brought into and out of contact with the valve seat d is installed in the primary chamber b and urged by a valve spring f to close the valve.
In the upper part of the valve body a is provided a pressure chamber h which is defined by a diaphragm g that acts as a pressure-activated member. A heat sensing tube (not shown) is connected to the pressure chamber h through capillary tube i. The operation of the diaphragm g in response to pressure changes in the pressure chamber h is transmitted to the needle valve disc e by a communication rod k that is connected to a contact plate j and passes through the valve opening I. Denoted m is an operating spring that opposes the pressure in the pressure chamber h and is installed between the contact plate j and a movable spring retainer n.
The valve body a is formed with an inclined adjust cylinder o in which an operating spring adjust screw p is installed so that it can be advanced and retracted. A front end surface p.sub.1 of the operating spring adjust screw p is in contact with a tapered driven surface n.sub.1 of the spring retainer n. Designated g is a seal ring and r a cap.
In the above construction, as the spring adjust screw p is advanced or retracted, the spring retainer n is moved up or down to change the compressive force of the operating spring m and thereby adjust the operating pressure of the diaphragm g.